This invention relates to heaters (hereinafter referred to as being of the kind specified) each comprising a heat store, electrical heating means for heating same, means providing for flow of air or other heat distributing fluid (herein for convenience referred to as air) into contact with the heat store and thereafter to a space or place to be heated, and flow control means for controlling the flow of such air.
The electrical heating means is ordinarily powered from an electrical supply source (herein called the off-peak supply) which is operative, i.e. rendered live, by time controlled switch means not accessible to the user for one or more restricted periods (herein called off-peak periods) during each basic 24 hour period. One of such off-peak periods which is frequently utilised extends from 2300 hrs. to 0700 hrs. and in some cases a second off-peak period is provided extending from 1300 hrs. to 1500 hrs.
During other periods (herein called on-peak periods) heat is required to be delivered from the heat store to the space to be heated and the temperature existing in this space during on-peak periods is often subjected to considerable short term fluctuations, e.g. the temperature may rise due to solar heating, especially when the space is bounded in part by an extensive glazed window area, and the temperature may fall sharply when there is a sudden decrease in weather temperature external to the space, especially when accompanied by high winds.
Heaters of the kind specified commonly include a flow control means in the form of a damper for controlling the flow of the heat distributing air and the position of the damper is determined by firstly the state of charge (temperature) of the heat store, and secondly by a user operated control. Control of the position of the damper as a function of state of charge is necessary to prevent a high flow rate of heat distributing air when the heat store is fully charged, partly because this could be unsafe and partly because it would be wasteful. The user control provides shift of the damper position (once it is open) to a position of greater or lesser opening as desired subjectively by the user.
When the user is absent, however, fluctuations in temperature in the space to be heated arising from factors such as those already mentioned are not catered for, and a user returning to the premises after a period of absence may find the space to be heated well above or well below the desired temperature.
One object of the present invention is to provide simple and reliable means capable of being manufactured at low cost and not requiring drawing of current from the on-peak supply for overcoming or mitigating this problem.